Lippo Vanni started his career producing finely painted images in manuscripts. A similar precision is evident here in Saint Peter's delicately painted flesh, expressive wrinkles and intricate robes.
The keys, inscribed ‘Authority’ and ‘Discernment’ in Latin, are the symbolic keys to heaven, which Christ entrusted to Peter. The saint in the small disc above holds a book, indicating that he is one of the four writers of the Gospels. His three companions must have featured on the other panels of a large altarpiece of which this work is a fragment.